Natural Hazards

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Natural Hazards
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Are all natural hazards natural?
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Introduction to Natural Hazards

• What is a Geohazard?
• Earth processes (involving the lithosphere,
  hydrosphere atmosphere) that, upon interaction
  with human populations, cause loss of life and
  property.
• It is important to understand the human element.
• Without it, there would be no hazard!
• Because of it, the science of geohazards becomes
  more important every year
• Mitigation - reduction/prevention

Hazardousconditionor result
geo-process
humanprocess
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Why is the human element so critical?

• The Earths population is increasing.
• More people living in hazard-prone areas.
• Populations are becoming more concentrated.
• For example
• Currently 6 billion people on Earth ( 50 live
  in cities).
• By 2025, estimated 8 billion people (66 in
  cities).
• Of these cities, 40 are coastal locations
• prone to severe storm and tsunami damage!
• And many major cities lie in areas subject to
  other geohazards (for example volcanoes and
  earthquakes).
• E.g., 12 of Earths population (720 million)
  lives within 100 km of a volcano that has erupted
  in the past 10,000 years.

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Global distribution of population vs location of
Holocene volcanoes
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• We CANNOT stop the geologic processes!
• We CANNOT stop our population growth

• Therefore, we must try to mitigate (reduce or
  prevent) the hazards through
• Scientific study of the geologic processes.
• Population education initiatives.
• Improvements in engineering/building practices.
• Management plans and hazard response scenarios.

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Types of Natural Hazards

• Volcanoes, floods, earthquakes, tornadoes,
  hurricanes, tsunamis, landslides, forest fires.
• Can adversely affect human populations.
• Can occur
• Without warning (e.g. earthquakes).
• With warnings (precursors) (e.g. satellite
  monitoring of hurricane tracks, or the presence
  of ground deformation at a volcano before an
  eruption).

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• To help forecast an event and thus mitigate the
  hazard we need to know
• Frequency vs. Magnitude
• Frequency (F) how often a given event occurs in
  a certain region.
• Magnitude (M) how powerful (amount of energy
  released) an event is.
• For example, high M hazards happen with low F,
  but are much more destructive.
• Scope
• Scope (S) area affected by a given hazard.
• Local - landslides, floods, earthquakes, fire
• Regional - tsunamis, small volcanic eruptions,
  larger earthquakes, hurricanes
• Global - large volcanic eruptions, global
  warming, large meteorite impacts

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Earthquakes and Tsunamis
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Frequency vs Magnitude
Magnitude Earthquake Effects Approx. number each year
lt 2.5 Usually not felt, but recorded 900,000
2.5-5.4 Often felt, only minor damage 30,000
5.5-6.0 Slight damage to buildings and other structures 500
6.1-6.9 May cause a lot of damage in very populated areas 100
7.0-7.9 Major earthquake. Serious damage. 20
gt 8.0 Great earthquake. Can be totally destructive near the epicenter. 1 every 5-10 years
Richter Scale Magnitudes
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San Francisco Great 1906 Earthquake

• Magnitude 7.8 earthquake.
• Epicenter only 3 km offshore.
• San Andreas fault ruptured over
• nearly 500 km.
• Considered one of the worst natural
• disasters in U.S. history.

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Earthquake Hazards

• Earthquakes are important hazards to understand
  because
• The natural hazard that, on average, kills the
  highest number of people per year (gt1 million
  during the past century).
• Commonly strikes without warning.
• No time for evacuation.
• No predictable trend to earthquake numbers,
  magnitude or location.
• 1000's of earthquakes every year worldwide.
• 20 are gt M7.0 and these account for 90 of the
  energy released and 80 of all the fatalities.

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How do we mitigate the hazard from earthquakes?

• Reinforce buildings
• (earthquakes dont kill people buildings
  do!)
• Education
• Disaster plan

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Earthquakes and Tsunamis

• An earthquake on the seafloor has the potential
  to form a tsunami.
• The earthquake must vertically displace overlying
  water (extensional or compressional faults - not
  transform).

Extension
Compression
Transform
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How does an earthquake form a tsunami?
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2004 South Asian Event

• Biggest earthquake since 1960 event in Chile.
  (M9.5)
• Magnitude 9.2
• 150 km off the west coast of Northern Sumatra
• Generated a disastrous tsunami that affected 12
  countries around the Indian Ocean.
• Travel time for the tsunami was 15 minutes to as
  long as 7 hours.
• So, there is the possibility of warning people
  ahead of time, but not by much!

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A village near the coast of Sumatra lays in ruin
after the tsunami.
- Estimated that 1,600 km of faultline slipped
about 15 m (a LOT of rock moved!). - The
earthquake released 20 x 1017 Joules of energy,
which is like setting off 475 million
kilograms of TNT or 23,000 atomic bombs!
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How do we mitigate the hazard from tsunamis?

• Monitoring
• The process is very technology-intensive
  (satellite monitoring, seismograph arrays,
  computer modeling and tracking of tsunamis).
• Costs are simply too high for many poorer
  countries.
• Often no technology is available to monitor local
  tsunamis.
• E.g., Papua New Guinea has no monitoring
  stations.
• Reliant on the Pacific Tsunami Warning Center (in
  Hawaii).
• Tsunami in 1998 was not detected because it
  originated locally.

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How do we mitigate the hazard from tsunamis?

• Establish building restrictions in hazard prone
  areas.
• In Hawaii, Hilo harbor and downtown were
  destroyed by the tsunamis of 1946 and 1960.
• The town is now rebuilt on higher ground and the
  devastated area is a park.

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How do we mitigate the hazard from tsunamis?

• Construction of seawalls.
• Cause early wave breaking away from populations.
• Thus prevent wave run up into urban areas.

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How do we mitigate the hazard from tsunamis?

• Public education
• Warning systems.
• Evacuation plans.
• Promote a general understanding of the hazards
  involved.

Punishment From God 45
Natural event 35
Bomb 20
Population reaction Papua New Guinea (1998)
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Tropical Storms
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• Atlantic and eastern Pacific Oceans Hurricanes
• - average 10 named storms/year, 6 become
  hurricanes
• Western Pacific Ocean Typhoons
• - average 16 named storms/year, 9 become
  typhoons
• Indian Ocean Cyclones (best term to describe
  these storms)
• Coriolis effect causes storms to circulate
  counterclockwise (northern hemisphere) or
  clockwise (southern hemisphere)
• Western Pacific warm waters, few land masses,
  major storms

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Hurricane Katrina (August 2005, Category 3) had
gale force winds extending 120 miles (190 km)
from the storm center (eye of the storm)
since these are circular storms this one was
approximately 240 miles (380 km) from one side to
the other and they can get much larger.
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Hurricane Ike (category 4) photo taken from 220
miles altitude in the space station. This
hurricane was 600 miles in diameter the largest
ever recorded.
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How do cyclones form?

• Tropical cyclones form only over warm ocean
  waters near the equator.
• Warm, moist air rises upward from the surface. As
  this air moves up it leaves less air near the
  surface. This causes an area of lower air
  pressure below.
• Air from surrounding areas with higher air
  pressure moves in to the low pressure area. Then
  this new cool air becomes warm and moist and
  rises, also. The cyclone is beginning to build
• As the warmed, moist air rises and cools the
  water in the air forms clouds. The whole system
  of clouds and wind spins and grows, fed by the
  oceans heat and water evaporating from the ocean
  surface.
• As the storm system rotates faster and faster, an
  eye forms in the center. It is very calm and
  clear in the eye, with very low air pressure.
  Higher pressure air from above flows down into
  the eye.
• When the winds in the rotating storm reach 39 mph
  (63 kmph), the storm is called a tropical
  storm.
• When the wind speeds reach 74 mph (119 kmph), the
  storm is officially a tropical cyclone (or
  hurricane or typhoon).
• Tropical cyclones weaken and eventually die out
  when they hit land, because they are no longer
  being fed by the energy from the warm ocean
  waters.

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How do cyclones form?
This figure shows the motions of air within
cyclones. The green arrows show where warm air is
rising. The red arrows indicate where cool air is
sinking.
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Classification of Cyclones
Category Wind Speed (mph) Damage at Landfall Storm Surge (feet)
1 74-95 Minimal 4-5
2 96-110 Moderate 6-8
3 111-130 Extensive 9-12
4 131-155 Extreme 13-18
5 gt 155 Catastrophic 19
The Saffir-Simpson Scale
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Hurricanes Typhoons - Cyclones

• The most widespread and destructive weather
  hazard that we face.
• - Example Hurricane Floyd (1999)
• Was only a moderate level hurricane (category 3
  at landfall).
• But, it caused 5.6 billion in damage in the
  Bahamas and North Carolina and 57 fatalities.
• 2.6 million coastal residents had to evacuate.
• Most rivers in Florida reached high-water levels
  equivalent to a 500-year flood.

Hurricane Floyd just before landfall.
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Cyclone Gorky - 1991

• Struck coast of Bangladesh.
• Wind speeds 250 km/hr (156 mph a category 5
  storm).
• A 6 meter (20 ft.) storm surge wave traveled
  several kms inland.
• Estimated 138,000 killed, and 10 million
  homeless.
• 2 billion dollars (2007) damage.

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Children attend class in what remains of their
school
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Homes in rural areas of poor countries are not
built to withstand 156 mph winds
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Hurricane Katrina - 2005

• Hurricane Katrina was the most costly and most
  deadly hurricane in the history of the USA.
• Category 5
• At least 1,836 fatalities.
• Damage estimated at 81.2 billion.

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Hurricane Katrina
Collapsed bridge in New Orleans
Suburbs in New Orleans
Boats washed onshore by the storm surge
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What type of damage is produced?

• Storm Surge
• Water that is pushed onshore by the force of the
  cyclone winds.

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What type of damage is produced?

• Wind of course.
• Responsible for the loss of power and utilities.
• Wind damage affects much larger areas than surge.
• Flying debris is a serious hazard.

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What type of damage is produced?

• Flying debris
• Can be propelled at very high speeds

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How do we mitigate the hazard from a cyclone?

• Monitoring
• Early warning systems.
• Infrastructure
• Cyclone walls.
• Communal shelters.
• Building codes.
• Education and planning

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Natural Hazards Summary
Graph showing the number of deaths per year due
to natural hazard events
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Economic losses due to major disasters are
increasing due to population growth and land-use
changes
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Number of major catastrophes are increasing due
to population growth and land-use changes are
there other reasons?
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http//maps.grida.no/go/graphic/trends-in-natural-
disasters

• Apparent exponential
• increase Why?
• Improved information
• transfer worldwide.
• Population growth.
• No change in number
• of volcanic eruptions,
• earthquakes, etc
• However, a statistically significant increase in
  cyclones and floods.
• Global warming???

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Population Growth and Natural Hazards?

Almost certain Population growth is a cause for increase in natural disasters. Under debate Population growth is an indirect trigger for some natural disasters, e.g., floods, cyclones (via global warming). We hope Better prediction and even artificially controlling some natural hazards.